1. Field of the Invention
This invention relates to a process making it possible to generate a marking signal, representative of the operation of various cylinders of an internal combustion engine having several cylinders, this signal being specifically intended for the control of an electronic fuel injection system of the sequential multipoint type.
The invention relates more specifically to a process for generating a signal making possible the marking of the position of each of the various cylinders in the course of their operating cycle and in particular their passing at the intake Top Dead Center position to phase the injection accurately.
2. Discussion of the Background
To improve the operation of internal combustion engines from the viewpoint of performances and from the viewpoint of the emission of pollutants, many fuel injection systems have been developed. Among them, it is possible to cite the multipoint indirect injection systems with electronic control, such as the RENIX system or such as the L (or LH)-Jetronic system marketed by the BOSCH company.
One of the essential characteristics of the multipoint electronic injection is its intermittent operation, the injectors are actually periodically actuated: at least once per engine cycle, or else in the case of a four-stroke engine once during two crankshaft revolutions or 720.degree. of angle. Two methods of opening the injectors have been developed: simultaneous actuation and sequential actuation.
Simultaneous or Full-Group injection consists in injecting the amount of fuel, determined by the electronic control device, by making all the injectors operate at the same time. The actuation of the injectors can be performed once per cycle (one injection every two crankshaft revolutions) or twice per cycle (one injection per crankshaft revolution). This last solution simplifies the management of the electronic control device which controls the injectors as a single control stage is necessary.
However, the Full-Group operating mode exhibits the drawback of injecting the fuel while an intake valve is still in an open position. Now, experience shows that the injection is not desirable when there is an open valve because it brings about an increase of emissions of pollutants as the injected fuel wets the plug and causes a poor initiation of the combustion.
Sequential injection consists in injecting the amount of fuel by actuating successively and in a given order the various injectors so as to inject best in each cylinder relative to the corresponding intake phase. The sequential injection is phased when the opening phase of each injector ends before the opening of the intake valve of the corresponding cylinder.
Phased sequential injection gives excellent results in terms of pollution control. Actually, the phased sequential injection makes it possible, by precisely controlling the moment of injection cylinder by cylinder, to eliminate under almost all operating conditions of the engine the direct injection of fuel in a cylinder by the open valve.
However, the multipoint electronic injection systems of the phased sequential type exhibit the drawback of producing a significant additional expense relative to a standard electronic injection installation of the "Full Group" type where all the injectors are activated simultaneously.
Actually, the phased sequential type systems particularly need to have very accurate means of marking the course of the engine cycle in each of the cylinders to make it possible for the electronic engine control unit to calculate and to control the output of each injector at a predetermined suitable moment, apart from the opening period of the corresponding valve.
It is customary, as is disclosed in French patent application FR-A-2,441,829, to mark, on a disk (or target) integral with the crankshaft, the angular position zones corresponding to-a determined phase of the stroke of the various pistons. The disk exhibits marking elements placed along its periphery, such as teeth of different length, and which in passing in front of a stationary receiving element generate electric impulses making it possible to produce a signal marking the passing at the Top Dead Center position of a specific piston.
Such a marking device proves insufficient, however, for performing the control of a phased sequential injection.
Actually, for a four-stroke internal combustion engine, the crankshaft executes two complete revolutions (or 720.degree. of angle) before a given piston regains the same operating position in the engine cycle. As a result, from observation alone of the rotation of the target integral with the crankshaft, it is not possible, a priori, to supply information on each cylinder without an uncertainty of two power strokes in the cycle (the marking of the Top Dead Center position covering both the intake phase and the firing phase).
Since the precise determination of the position of each cylinder in the cycle is not able to be deduced from the rotation of the crankshaft alone, a search for additional information is therefore necessary to know whether the cylinder is in the first or in the second half of the engine cycle (intake then compression phases during the first crankshaft revolution, firing and expansion phases during the second revolution).
To obtain such additional information, marking elements carried by a transmitting disk which rotates two times slower than the crankshaft are conventionally used. For this purpose, it is possible to place this transmitting disk on the camshaft or else on the shaft of the ignition distributor which is driven by a reduction gear of ratio 1/2 from the crankshaft.
Conventionally therefore, the camshaft (or else the driving pulley of the camshaft) is equipped with a target showing a reference point which works with a stationary sensor for delivering a frequency signal equivalent to "1" during the first half of the cycle and "0" during the second half. The combination of signals coming from the crankshaft sensor and from the camshaft sensor makes it possible for the system to control a phased sequential injection.
Such angular marking systems using both a crankshaft sensor and a camshaft sensor are relatively bulky, costly, and have a delicate assembly. Further, in the case where one of the sensors breaks down, i.e., in a degraded operating mode of the engine, the conventional measuring systems do not make it possible to provide enough information on the control system of the electronic injection of the engine, hence a risk of misadjustment of the latter.